Method and semi-finished item for producing composite products and the products thus obtained

ABSTRACT

A semi-finished item which can be used in this method and to a product made using this method and/or with this semi-finished item.

TECHNICAL FIELD

This invention relates to a method for producing composite productscomprising layers of fibres, specifically layers of carbon fibrefabrics. This description also relates to a semi-finished item which canbe used in this method and to a product made using this method and/orwith this semi-finished item.

BACKGROUND ART

As is known, the RTM (Resin Transfer Moulding) method can be used toproduce parts from composite materials comprising carbon fibre fabrics.In this known method, one or more superposed layers of dry fabric, thatis to say, fabric which is substantially not impregnated with resins,are placed between two matching moulds into which a resin mixed with ahardener is injected under high pressure in such a way that the resinpolymerizes in the mould to obtain the finished product.

In a variant of this method, known as RTM-L (RTM-Light), the resin isinjected at a lower pressure so as to increase the working life of themoulds and thus reduce investment costs.

While the resin is being injected, however, in the RTM and RTM-Lmethods, the fibres of the fabric layers, especially the outer layers,are displaced on account of the resin pressure gradients at theimpregnation stage, with consequent loss of weave regularity, worseningthe aesthetic aspect of the final product.

In another prior art method, fabrics previously impregnated with resinknown as prepreg are used. These are reheated and pressed on at leastone mould without injecting further resin. This prior art method allowsobtaining composite products whose outer layers maintain weaveregularity even after resin polymerization. It is, however, moreexpensive than the RTM method and, precisely because of pre-impregnationof the layers, the structural properties of the products made are not asgood.

AIM OF THE INVENTION

This disclosure therefore has for an aim to provide a method which isfree of the above mentioned disadvantages. This aim is achieved by amethod and a semi-finished item whose main features are specified in theappended claims.

Thanks to the method of this disclosure, it is possible to makecomposite material parts having a good aesthetic appearance andexcellent structural properties using dry fibre fabrics and moulds intowhich resin and hardener are injected. This method can therefore beautomated at least partly, thanks also to the semi-finished item of thisdisclosure, which can be prepared during a preliminary stage. In effect,at least one outside surface of the product thus obtained comprises afabric whose weave is substantially regular and whose high visualquality meets the high standards of the automotive industry, such as,for example, the “Class A” standard.

Thus, whereas prior art RTM methods cannot guarantee products with highaesthetic features on account of the deformation and displacement of thefibres of the outer layer during resin injection, the method of thisdisclosure allows obtaining products whose appearance is the same asthat obtained using prepreg methods. This method therefore combines theadvantages of reduced production time and excellent mechanicalproperties typical of RTM methods with the improved aesthetic finish ofproducts made using prepreg methods.

These advantages are obtained above all thanks to the layer ofnon-polymerized resin which causes the outer fabric layer to adhere to afunctional surface of the mould prior to injection of the resin whichimpregnates this fabric layer and the structural layers superposedthereon. Further, the hardener injected with the resin is sufficient inquantity to also polymerize the resin applied on the fabric layer.

Thanks also to a thermoplastic film applied between the fabric layer anda structural layer adjacent thereto, the fabric layer is held moresecurely in the correct position during resin injection.

The present method is further simplified using a semi-finished itemcomprising the fabric layer, the layer of resin substantially free ofhardener and the thermoplastic film. The semi-finished item can beeasily cut into predetermined shapes and even stored for use at a laterstage. The product obtained using this method or semi-finished item canbe distinguished from prior art products made of composite materialthanks to the presence of the thermoplastic film between the outerfabric layer and the adjacent structural layer.

During certain specific steps of the method, the fabric layer and thestructural layer are pressed and/or heated on at least one mould inorder to improve the bond between these layers before the resin isinjected, thus obtaining a better final product.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages and features of the method, semi-finished item andproduct according to this invention will become clearer to those wellversed in the trade from the following detailed, non-limitingdescription of an embodiment with reference to the accompanyingdrawings, in which:

FIG. 1 is a schematic view of a preliminary operating step of thismethod;

FIG. 2 is an enlarged cross section of the semi-finished item obtainedfrom the preliminary operating step;

FIGS. 3, 5, 7, 9, 11, 13, 15 and 17 are schematic cross sections offurther operating steps of the method;

FIGS. 4, 6, 8, 10, 12, 14, 16 and 18 are enlarged views of the detailsIV, VI, VIII, X, XII, XIV, XVI and XVIII from FIGS. 3, 5, 7, 9, 11, 13,15 and 17, respectively.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 shows a preliminary operating step of the method for making asemi-finished item, whereby at least one layer 1 of fibre fabric ispreferably pressed, for example with a calender 2, in such a way as toeliminate all gaps between weft and warp and to increase yarn tension soas to make the fabric structure more compact. The fabric layer 1 ispreferably a fabric of fibres for composite materials, specificallycarbon fibres, having a substantially uniform weft and/or a thickness ofbetween 0.1 and 0.8 mm, specifically between 0.2 and 0.3 mm: forexample, a carbon fibre fabric with “Twill”, “Plain”, “Satin”,“Braided”, “Unidirectional” or other type of uniform and/or regularweave pattern, specifically having a grammage of between 230 and 260g/m2. Preferably, the fabric of the fabric layer 1 is substantially dry,that is, it contains a quantity of additives, such as adhesives orfixatives, which is less than 10% by weight. At least one layer ofnon-polymerized, composite material resin 3, substantially free ofhardener, specifically an epoxy resin, is applied on at least onesurface of the outer layer 1, in particular by means of a nebulizer 4.The resin 3 may, for example, be XB 3518 resin made by HuntsmanCorporation, and is applied on the outer layer 1 in a quantity ofbetween 2% and 7% by weight of the outer layer 1, specifically between 5and 19 g/m2, and more specifically, approximately 12 g/m2. A protectivesheet 5, specifically of plastic material such as Mylar, for example,which does not absorb humidity and thus does not shrink if ambienthumidity varies, is applied by a calender 6 on the surface of the fabric1 provided with the resin 3, which is thus covered by the protectivesheet 5. This prevents creases from forming in the fabric 1 and keepsthe layer of resin 3 in its original state, substantially unchanged byambient conditions, in particular by preventing the polymerizationprocess from starting. Therefore, since the resin 3 is not activated,the protective sheet 5 is applied removably on the layer of resin 3.

A thermoplastic film 7, preferably comprising at least one mesh ofnylon, polypropylene, ABS, PLA, polycarbonate or polyethyleneterephthalate is applied by a calender 8 on the surface of the outerlayer 1 opposite to the surface which is provided with the resin layer3. The fabric layer 1 thus obtained is then cut into a predeterminedshape by a cutting machine 9 and the resulting semi-finished item 10 canbe rolled up and/or enclosed in a sealed bag 11 to prevent contaminationby external agents, such as humidity or volatile carbon during storage.

FIG. 2 shows the semi-finished item 10 comprising the fabric layer 1which is provided with the resin layer 3 covered by the protective sheet5, joined to the thermoplastic film 7 and inserted in the bag 11.

With reference now to FIGS. 3 and 4, it may be observed that in a firststep of the method, the semi-finished item 10 is extracted from the bag11, separated from the protective sheet 5 and placed on a first mould 12whose functional surface is preferably convex and/or made of compositematerial, in particular containing carbon fibre, with the resin layer 3positioned between the outer layer 1 and the first mould 12. Thethermoplastic film 7 is thus on the side opposite the first mould 12.

With reference now to FIGS. 5 and 6, it may be observed that in the nextstep of the method, the outer layer 1 is covered with a vacuum sack 13and pressed onto the first mould 12 by pumping the air out so that theair pressure inside the vacuum sack 13 is reduced, in particular below130 mbar. The vacuum sack 13 comprises a non-perforated peeling film 14to prevent suction from being applied to the resin 3 deposited on thefabric 1, as well as a nylon bleeder 15 whose grammage is lower than thegrammage of prior art bleeders used in prepreg methods, specifically agrammage less than 180 g/m2, and more specifically, approximately 170g/m2.

With reference now to FIGS. 7 and 8, it may be observed that in the nextstep of the method, the vacuum sack 13 is removed from the outer layer 1and at least a first inner fibre layer 16, preferably comprising one ormore dry carbon fibre fabrics for structural applications, is applied onthe outer layer 1. In particular, the first inner layer 16 has agrammage of between 700 and 900 g/m2 and/or a thickness of between 1 and8 mm. At least one spacer 17 made of plastic material, preferablyexpanded plastic material, may be placed on the first inner layer 16,which is then covered completely or partly by the spacer 17. At leastone surface of the first inner layer 16, specifically the surfaceopposite the outer layer 1, may be provided with a binder 18 forexample, thermoplastic wires mixed with the carbon fibres or an adhesivefilm.

With reference now to FIGS. 9 and 10, it may be observed that in thenext step of the method, the outer layer 1 and the first inner layer 16,with the spacer 17, if present, may be covered with a vacuum sack 19 forexample, one that is the same as the vacuum sack 13 and pressed onto thefirst mould 12 by pumping the air out. At the same time, the layers 1and 16 are heated to a temperature between 70° and 90° C., for exampleby infrared radiators, in such a way as to compress and at least partlymelt the thermoplastic film 7 to join the outer layer 1 to the firstinner layer 16 and the first inner layer 16 to the spacer 17 by means ofthe binder 18.

With reference now to FIGS. 11 and 12, it may be observed that in thenext step of the method, the vacuum sack 19 is removed from the firstinner layer 16 and at least a second inner layer 20, preferablycomprising one or more dry carbon fibre fabrics for structuralapplications, can be applied on the first inner layer 16 and/or on thespacer 17, if present. In particular, the second inner layer 20 has agrammage of between 700 and 900 g/m2 and/or a thickness of between 1 and8 mm. At least one surface of the second inner layer 20, specificallythe surface facing the outer layer 1, may be provided with a binder 21for example, thermoplastic wires mixed with the carbon fibres or anadhesive film.

With reference now to FIGS. 13 and 14, it may be observed that in thenext step of the method, the outer layer 1 the first inner layer 16 andthe second inner layer 20, with the spacer 17, if present, may becovered with a vacuum sack 22 for example, one that is the same as thevacuum sack 13 and pressed onto the first mould 12 by pumping the airout. At the same time, the layers 1, 16 and 20 are heated to atemperature between 70° and 90° C., for example by infrared radiators,in such a way as to join the second inner layer 20 to the spacer 17 bymeans of the binder 21.

With reference now to FIGS. 15 and 16, it may be observed that in thenext step of the method, the outer layer 1 the first inner layer 16 andthe second inner layer 20, with the spacer 17, if present, are coveredby at least a second mould 23 in such a way that the layers 1, 16 and 20are positioned at least between the first mould 12 and the second mould23 in a cavity which is hermetically closed by at least one perimeterseal placed between the moulds. Preferably, the functional surface ofthe second mould 23 is concave and/or made of composite material, inparticular containing carbon fibre. The moulds 12, 23 are then fixed toeach other and heated for example in an oven at a temperature of between45 and 90° C. after which resin and hardener are injected between themoulds 12, 23 through at least a first nozzle 24 in order to impregnatethe layers 1, 16, 20. At the same time, air is extracted from the moulds12, 23 through at least a second nozzle 25 in the same way as, forexample, in an RTM method. The nozzles 24 and/or 25 are preferablypositioned at least at one edge of the layers 1, 16 and/or 20 so thatinjection and/or extraction occur in directions which are substantiallytangential to that edge.

The hardener mixed with the resin injected through the first nozzle 24comprises a first quantity of hardener sufficient to polymerize thisresin and a second quantity of hardener sufficient to also polymerizethe resin 3 applied on the outer layer 1. Preferably, the resin injectedinto the moulds 12, 23 is the same as the resin 3 applied on the outerlayer 1, specifically an epoxy resin such as, for example, XB 3518 resinmade by Huntsman Corporation. Preferably, the first and secondquantities of hardener include a hardener which is compatible both withthe injected resin and with the resin 3, specifically a single aminehardener such as, for example, Aradur® 22962 hardener made by HuntsmanCorporation.

Preferably, the first quantity by weight of hardener mixed with theinjected resin is between 20% and 30% by weight of the quantity byweight of the injected resin, whilst the second quantity by weight ofadded hardener for the resin 3 is between 1.5% and 55% of the firstquantity.

With reference now to FIGS. 17 and 18, it may be observed that after theinjected resin has impregnated the layers 1, 16 and 20 and haspolymerized thanks to the injected hardener, and that the resin 3 on thelayer 1 has also polymerized, also thanks to the injected hardener, thefinished part 26 which includes the outer layer 1, the thermoplasticfilm 7, one or more inner layers 16, 20, and, if necessary, at least onespacer 17, is extracted from the moulds 12, 23 and fine finished foruse.

Variants or additions to the embodiment illustrated and described hereincan be made by experts in the trade without departing from the scope ofthe claims appended hereto. In particular, further embodiments maycomprise the technical features of one or more of the appended claimswith the addition of one or more technical features described in thetext or illustrated in the drawings, taken individually or in anycombination.

1. A method for producing products made of composite material, whereinit comprises the following operating steps: placing between a firstmould and at least a second mould at least one layer of compositematerial fibre fabric and at least a first layer of composite materialfibres, wherein a layer of non-polymerized, composite material resin,substantially free of hardener, is placed between the fabric layer andthe first mould; injecting resin and hardener between the first mouldand the second mould to impregnate the layer and the first fibre layerwith the injected resin and polymerizing the injected resin and theresin layer with the injected hardener.
 2. The method according to claim1, wherein at least one thermoplastic film is placed between the layerand the first fibre layer.
 3. The method according to claim 1, whereinat least a second fibre layer is placed between the first fibre layerand the second mould before injecting the resin between the first mouldand the second mould, so that the second fibre layer is also impregnatedwith the injected resin.
 4. The method according to claim 1, wherein atleast one spacer is placed between the first fibre layer and the secondfibre layer before injecting the resin between the first mould and thesecond mould.
 5. The method according to claim 1, wherein the resinlayer is applied on the fabric layer before placing the fabric layer onthe first mould.
 6. The method according to claim 1, wherein the resinlayer is in contact with the first mould when the fabric layer is placedbetween the first mould and the second mould.
 7. The method according toclaim 1, wherein the hardener injected between the first mould and thesecond mould comprises a first quantity of hardener sufficient topolymerize the injected resin and a second quantity of hardenersufficient to also polymerize the resin placed on the fabric layer. 8.The method according to claim 1, wherein before injecting the resinbetween the first mould and the second mould, the fabric layer iscovered with a vacuum sack and pressed onto the first mould by pumpingthe air out, wherein the vacuum sack comprises a non-perforated peelingfilm.
 9. The method according to claim 2, wherein before injecting theresin between the first mould and the second mould, the fabric layer andthe first fibre layer are covered with a vacuum sack, pressed onto thefirst mould and heated in such a way as to compress and at least partlymelt the thermoplastic film to join the outer layer to the first fibrelayer.
 10. The method according to claims, claim 1, wherein the fabriclayer is pressed before being placed between the first mould and thesecond mould.
 11. The method according to claim 1, wherein the resin isinjected between the first mould and the second mould through at leastone nozzle disposed at least at one edge of the fabric layer or of thefirst layer so that resin injection occurs in a direction which issubstantially tangential to that edge.
 12. The method according to claim1, wherein when the resin is injected between the first mould and thesecond mould, air is extracted from the moulds through at least onenozzle disposed at least at one edge of the fabric layer or of the firstlayer so that air extraction occurs in a direction which issubstantially tangential to that edge.
 13. The method according to claim1, wherein the resin injected between the first mould and the secondmould is the same as the resin applied on the fabric layer.
 14. Aproduct made of composite material, comprising polymerized resin whichincludes at least one layer of composite material fibre fabric and atleast a first layer of composite material fibres, wherein at least onethermoplastic film is placed between the fabric layer and the firstfibre layer.
 15. The product according to claim 14, wherein the firstfibre layer or the second fibre layer comprises one or more dry carbonfibre fabrics, has a thickness of between 1 and 8 mm and or a grammageof between 700 and 900 g/m2.
 16. A semi-finished item for producingcomposite material products and comprising at least one layer ofcomposite material fibre fabric, wherein at least one layer ofnon-polymerized, composite material resin, substantially free ofhardener, is applied on at least one surface of the fabric layer and inthat at least one thermoplastic film is applied on the surface of thefabric layer opposite to the surface provided with the resin layer. 17.The semi-finished item according t claim 16, wherein a protective sheetis applied removably on the resin layer.
 18. The method according toclaim 2, wherein the thermoplastic film comprises a mesh of nylon,polypropylene, ABS, PLA, polycarbonate or polyethylene terephthalate.19. The method according to claim 2, wherein the fabric layer comprisesa dry carbon fibre fabric with a substantially uniform weave pattern.20. The method according to claim 2, wherein the fabric layer has athickness of between 0.2 and 0.3 mm and/or a grammage of between 230 and260 g/m2.
 21. The method according to claim 2, wherein the resin layeris applied on the fabric layer in a quantity of between 2% and 7% byweight of the fabric layer.